High intensity discharge lamps (hereinafter HID lamps) are often employed where high levels of relatively efficient lighting are needed; as, for example, in sports stadiums, along freeways and the like. An example of such lamps is the high efficiency metal halide HID lamp typically employing a mixture of noble gases including xenon and argon, plus mercury vapor, and a variety of metal halide vapors which are blended to obtain greater output and improved spectral content in the light produced by the lamp, such gases typically being under pressure within a transparent (e.g., quartz envelope). Examples are those which are generally available from Venture Lighting Company under designators MPDC48/C/BU and MPDC68/C/BU. Other examples are high pressure sodium and mercury vapor lamps.
Although such lamps efficiently provide high levels of light output per unit of input electrical energy, they typically exhibit characteristics that complicate and/or discourage their use and control. Thus, for example, such lamps tend to exhibit unstable arc voltages, especially when operated at low power levels. In addition, such lamps tend to fail violently at the ends of their lives, such failure being attributable to arc voltage (and consequently power in conventional systems) that tend to increase throughout the useful lives of the lamps, thus leading to corresponding increases in dissipated power, excessive temperature and internal pressure. Still other problems include:
1. Differing characteristics exhibited by nominally similar lamps; PA1 2. Coordinating control of multiple lamps; PA1 3. Starting and re-starting lamps when cold, warm or hot; PA1 5. Satisfactorily dimming arc lamps while maintaining stability; and PA1 6. Excessive time required for starting.
4. Maintaining light output at selected levels;
A variety of proposals have heretofore been made for controlling gaseous discharge high efficiency lamps, illustrative of which are those set forth in U.S. Pat. No. 5,623,187 to Paulo Caldeira et al.; U.S. Pat. No. 5,589,742 to Hiroyuki Ueda; U.S. Pat. No. 5,550,434 to Kenneth J. King et al; U.S. Pat. Nos. 5,036,256, 5,051,665, and 5,391,966 to Robert L. Garrison; and U.S. Pat. No. 5,523,656 to Meerten Luursema. Although the proposals of these and other patents have addressed selected ones of the foregoing characteristics, there yet remain unresolved drawbacks to their use. Thus, for example, among other problems, there have continued to be problems with excessive starting time, re-starting while a lamp is still hot and before it has cooled to ambient temperature, the aforementioned inherent arc instability and build-up of arc voltage as lamps age.
Although various of the foregoing problems have been partly addressed by prior proposals, there has yet continued to be a need for a comprehensive arc discharge lamp control system that provides solutions to each of the foregoing difficulties, and while other prior patents make reference to various constant wattage calculating and regulating functions, none that are known to the inventor hereof reveal a specific, workable, circuit topology for achieving such power calculation.